1. Field of the Invention
The present invention relates to an inter-image operation method and an inter-image operation apparatus for carrying out an inter-image operation, and to an image display method and an image display apparatus for displaying an image obtained by using the above inter-image operation method or apparatus. More specifically, the present invention relates to an improved method and apparatus for carrying out an operation between two or more sets of base image data each representing a distinct base image of an identical object, and to an improved method and apparatus for displaying an image obtained by using the above method or the apparatus for carrying out the operation.
2. Description of the Related Art
The technique of comparing two or more base images of an identical object has been used in various fields to discover differences between those base images for, e.g., examining the object based on the differences.
For example, in the field of manufacture, the above technique has been used to search those portions of a product where improvement in endurance is desired by comparing two base images, one being an image of a new product and the other being an image of the same product after an endurance test, and determining those portions where great differences are observed between the two base images. In the medical field, as another example, the technique has been used by doctors to follow progress of disease or stages of a cure and plan the most suitable course of treatment by comparing a plurality of radiation images of the same diseased part of a patient taken at different points in time.
When using the technique of comparing two or more base images as is used on a daily basis in various fields, those two or more base images are often displayed on an image display etc. or outputted onto a film or the like using a printer. Before displaying or outputting the images, the images are converted to image density signals or luminance signals.
The two or more base images themselves may be displayed or outputted simply in a row or a column for comparison. However, the point of the greatest interest for the examiner is the difference between the base images, and it would be difficult for the examiner to discover a minor difference watching the base images themselves displayed or outputted in a row or a column.
In this respect, to improve the efficiency of image comparison, there has been a commonly-used method of extracting and enhancing the difference between two or more base images by matching positions in the base images and conducting inter-image operations including a subtraction operation between the images (see, for example, Japanese Patent Application No. 11(1999)-342900). Such a method of extracting and enhancing the difference between the base images helps the examiner recognize the difference accurately and avoid the risk of overlooking the progress or cure of the diseased portion.
However, the inter-image operation as described above is generally a quite time-consuming operation because it consists of a series of operations (e.g., position-matching operations) between a number of pixels. Moreover, although the image obtained through the inter-image operation (hereinafter, referred to as a processed image) is often used repeatedly in the course of treatment, the image has usually been recalculated upon each diagnosis. Thus, the examiner has been required to wait for a certain time in each diagnosis until the processed image appears on the image display etc., and such a situation has been an obstacle to efficient diagnosis.